Magnetic sensor using a parametrically excited second harmonic oscillator

ABSTRACT

A magnetic sensor using a parametrically excited second harmonic oscillator for detecting a minute magnetic field by utilizing a change in the phase of the second harmonic of the oscillator in accordance with the direction of an external magnetic field. At least three inductance elements each formed with a magnetic wire member and its winding are employed for forming the parametrically excited second harmonic oscillator, one of the three inductance elements being a main element and the others auxiliary elements, the auxiliary elements being disposed about the main element. The windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other, so that a sensitivity characteristic against an external magnetic field is made extremely sharp with respect to a head portion of one end of the main element.

United States Patent 1191 Watanabe et al.

[ Jan. 29, 1974 1 1 MAGNETIC SENSOR USING A PARAMETRICALLY EXCITEDSECOND HARMONIC OSCILLATOR [75] Inventors: Teruji Watanabe, Niza;Takasuke Fukui, Tokyo; Shizuo Suzuki, Kawasaki, all of Japan [73]Assignee: Kokusai Denshin Denwa Kabushiki Kaisha, Tokyo, Japan [22]Filed: Oct. 16, 1972 [21] Appl. No.: 298,008

[30] Foreign Application Priority Data Primary Examiner-James W. MoffittAttorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato [5 7]ABSTRACT A magnetic sensor using a parametrically excited secondharmonic oscillator for detecting a minute magnetic field by utilizing achange in the phase of the second harmonic of the oscillator inaccordance with the direction of an external magnetic field. At leastthree inductance elements each formed with a magnetic wire member andits winding are employed for forming the parametrically excited secondharmonic oscillator, one of the three inductance elements being a mainelement and the others auxiliary elements, the auxiliary elements beingdisposed about the main element. The windings of the elements beinginterconnected in series in such a manner that when the same excitingvoltage is applied to the magnetic members a magnetic field establishedby a second harmonic current flowing in the winding of the main elementand a magnetic field by the second harmonic current flowing in thewinding of each auxiliary element may be opposite in direction to eachother, so that a sensitivity characteristic against an external magneticfield is made extremely sharp with respect to a head portion of one endof the main element.

5 Claims, 19 Drawing Figures PATENTED JAN 2 9 I974 SHEET 1 BF 4 PRIOR AR7 PR] OR AR T PATENTEI] JAN 2 91974 SHEET 3 BF 4 Fig. 5F

PATENTED 3, 789,234

sum u 0F 4 MAGNETIC SENSOR USING A PARAMETRICALLY EXCITED SECONDHARMONIC OSCILLATOR This invention relates to a magnetic sensor in whicha parametrically excited second harmonic oscillator is formed with amagnetic wire member having a magnetic film disposed on a conductor sothat a small magnetic field is detected by a change in the oscillationphase of the second harmonic oscillator.

Conventional magnetic sensors of the type, such as disclosed in JapanesePat. No. 45-10031, have a defect that a narrow sensing beamcharacteristic is difficult to obtain because of their construction.

An object of this invention is to provide a magnetic sensor using aparametrically excited second harmonic oscillator, which provides anextremely narrow sensing characteristic.

To attain the above object of this invention, a magnetic sensor using aparametrically excited second harmonic oscillator is provided in whichat least one inductance element is formed with a magnetic wire memberhaving a magnetic film deposited on a conductor and a winding woundthereon; in which a capacitor is connected in parallel with the windingto constitute a resonance circuit; and in which an AC exciting currentis applied to the magnetic wire member to produce a second harmonic ofthe exciting current in the resonance circuit; whereby a minute magneticfield is detected by utilizing a change in the phase of the secondharmonic in accordance with the direction of an external magnetic field.

In accordance with the principle of this invention, at least threeinductance elements each formed with a magnetic wire member and itswinding are employed, one of the three inductance elements being a mainelement and the others auxiliary elements; the auxiliary elements beingdisposed about the main element; and the windings of the elements beinginterconnected in series in such a manner that when the same excitingvoltage is applied to the magnetic members a magnetic field establishedby a second harmonic current flowing in the winding of the main elementand a magnetic field by the second harmonic current flowing in thewinding of each auxiliary element may be opposite in direction to eachother, whereby a sensitivity characteristic against an external magneticfield is made extremely sharp with respect to a head portion of one endof the main element.

The principle, construction and operations of this invention will beunderstood from the following detailed discussion taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a diagram showing the construction of a conventionalparametric magnetic sensor;

FIG. 2 is a diagram illustrating the construction of a conventionalparametric magnetic sensor of differential type designed to avoid theinfluence of an external uniform magnetic field;

FIGS. 3A, 33, 4A, 4B and 4C are diagrams showing examples of thisinvention and their magnetic sensitivity distribution curves;

FIGS. 5A to 5G, 6A to 6C and 7 are diagrams illustrating other examplesof this invention constructed in the form of modules respectively; and

FIG. 8 is a characteristic diagram showing experimental examples of themagnetic sensitivity distribution curves of the parametric magneticsensors of this invention and the prior art respectively.

For clearly describing the difference between the conventional arts andthis invention, conventional devices are previously described.

A conventional device of this kind is constructed as shown in FIG. 1 or2. FIG. 1 illustrates a single-type magnetic sensor (refer to JapanesePat. No. 45-10031). Reference numeral 3 indicates a magnetic wire memberhaving a magnetic film deposited on a conductor in such a manner as tohave an easy magnetization direction in its circumferential direction,and 4 an oscillation winding wound on the magnetic member 3.

The magnetic member 3 and the winding 4 make up an inductance element L.Reference numerals 1 and la designate exciting terminals, to which anexciting voltage e, ofa frequencyfis applied, 2 and 2a output terminals,and reference character C identifies a capacitor connected in parallelwith the winding 4. The inductance element L and the capacitor Cconstitute a resonance circuit of a frequency 2f. Accordingly, if theresonance circuit is excited with the exciting voltage e, between theinput terminals 1 and la, a second harmonic voltage 2 is producedbetween the output ter minals 2 and 2a.

In this case, if the intensity of magnetic field (for example, amagnetic field from a magnetizer M) acting on a head H which is eitherone of both ends of the magnetic member 3 is in excess of a certainvalue, the oscillation phase of the voltage e is dependent on thedirection of magnetic flux in the magnetic field. The sensitivitydistribution curve of the magnetic sensor in this case is dipole-shapedas indicated by a reference numeral 5 in FIG. 1 but only the half circleon the outside of the head H (on the right of the line YYa) isconsidered for the sake of brevity.

FIG. 2 shows the construction of a differential type magnetic sensor,which employs an inductance element consisting of magnetic wire members3 and 3a and a winding 4 as is the case with the example of FIG. I. Thesensitivity distribution curve of this magnetic sensor is substantiallysemi-circular on the right of the line YYa as indicated by referencenumerals 9 and 9a in FIG. 2, as is the case with the example of FIG. 1,but, at a point 10 between the two magnetic members 3 and 3a, the actionon the magnetic members 3 and 3a is in equilibrium and sensitivity isthe infinitesimal.

For example, if the region 9 is a region in which the oscillation phasereverses from 0" to 1r, the region 9a is that in which the phasereverses from 'n'" to 0". The single type oscillation element of FIG. 1is subject to the influence of an external uniform magnetic field,whereas the differential type oscillating element of FIG. 2 is adaptedto avoid the influence of the external uniform magnetic field. However,either oscillating element has a defect that a narrow sensing beamcharacteristic is difficult to obtain.

FIG. 3A shows one example of this invention, which employs threeinductance elements (hereinafter referred to as elements): the centralone is a main element and the others are auxiliary elements and in whichthe elements are disposed in a two-dimensional plane with the auxiliaryelements spaced a suitable distance (D) apart from the main element 9and one end of the main element is used as a head H. In this case, thewinding wound on the main element 9 is positioned as close to the head Has possible and those on the auxiliary elements 10 and 11 are a suitabledistance (d) apart from the head H of the main element 9. The windingsof these elements are interconnected in series so that a magnetic fieldgenerated by a current flowing in the main element 9 and those in theauxiliary elements 10 and 11 may be opposite to each other, and acapacitor C is connected in parallel with the seriesconnected windingsto constitute an oscillator circuit. Further, no limitation is set onthe direction of the exciting current but it is effective for narrowingthe beam width if the magnetic wire members of the respective elementsare interconnected in series in such a manner that the exciting currentflowing in the magnetic wire member of the main element 9 and thoseflowing in the magnetic wire members of the auxiliary elements 10 and IImay be opposite in direction to each other. It is preferred to selectthe numbers of turns of the winding of each element so that the sum ofthe number of turns of the windings of the auxiliary elements may beequal to that of the main element.

Various constructions are considered for applying the exciting voltagee, to the magnetic wire members forming the respective elements. Forexample, it is possible to apply the voltage to the magnetic wiremembers interconnected in parallel as depicted in FIG. 3B.

In the magnetic sensor thus constructed, if the exciting voltage e,isapplied between the terminals 1 and 1a, the second harmonic voltage e isproduced between the output terminals 2 and 2a in the same manner asthat in the prior magnetic sensors described previously. Under suchconditions, a second harmonic field by the second harmonic voltage e andan internal DC magnetic field by the second harmonic magnetic field areestablished in each element but the internal DC magnetic field in themain element 9 and those in the auxiliary elements 10 and l] are reversein direction from each other. Then, when the magnetizer M is placed inthe neighborhood of the head H, if a magnetic field being established bythe magnetizer M is large and opposite in direction to the internalDCmagnetic field in the main element 9, the oscillation phase of theaforementioned second harmonic voltage reverses from O to 1r or viceversa and the internal DC magnetic field also reverses correspondingly.

Further, in response to the reversal of the oscillation phase of thesecond harmonic voltage and the internal DC magnetic field in the mainelement 9, those in the auxiliary elements 10 and 11 also reverse. It isdesirable that the oscillation phase of the second harmonic voltage ineach element is restored to its original one when the magnetizer M ismoved away from the head H.

Means for restoring the oscillation phase may be, for example, of such aconstruction that a small magnet is attached to the opposite end of themain element 9 from the head H or that another winding is wound on themain element 9 and supplied with a minute DC cur rent.

If the magnetizer M is moved away from the head H toward the auxiliaryelement 10, the magnetic fields established by the magnetizer M in themain element 9 and the auxiliary element 10 are in the same directionbut the intensity of the field in the element 9 is low, while that inthe element 10 is high. In this case, since the internal DC magneticfield and the magnetic field by the magnetizer M in the element 10 areopposite in direction from each other, if the magnetic field by themagnetizer M is appropriately larger than the internal one by the secondharmonic voltage, the oscillation phase can be reversed. Thus, themagnetic effect of the magnetizer M acts on the main element 9 and theauxiliary ones 10 and 11 in reverse directions, so that there exists apoint intermediate between the elements 9 and 10 or 9 and 111 where themagnetic force of the magnetizer M applied to the main element 9 tocontribute to the reversal of the oscillation phase is in equilibriumwith that applied to the auxiliary element 10 or 11 to contribute toholding of the oscillation phase. Since this point is independent of themagnitude of the magnetic force of the magnetizer M, the directivitycharacteristic of the sensitivity distribution curve can be narrowed bydecreasing the distances (D) between the main element 9 and theauxiliary elements 10 and 11. For example, by selecting the diameter ofthe magnetic wire member of the main element 9 to be 0.5mm and reducingthe distances (D) between the main element 9 and the auxiliary elements10 and I] as short as possible, the sensitivity distribution curve canbe made extremely narrow.

FIG. 4A shows another example in which the twodimensional constructionof FIG. 3A or 3B is rendered into a three-dimensional one. The operationof this example is the same as that in the case of FIG. 3A or 3B and itsdetected distribution curve can be expressed in a cubic form such asdepicted in FIG. 48. FIG. 4C illustrates the arrangement of therespective elements viewed from a direction Z, that is, from thedirection of the head of the main element. FIG. 4A shows an example inwhich four auxiliary elements are symmetrically arranged about the mainelement 9 but the num ber of the auxiliary elements is not limitedspecifically to four but may be two as depicted in FIG. 3A or 3B or morethan two. It is sufficient for the purpose to dispose the auxiliaryelements along the peripheral surface of a cylinder drawn about the mainelement and connect their magnetic wire members and windings asdescribed previously in connection with FIGS. 3A, 38, 4A, 4B and 4C.

In order to provide for a further enhanced sharp directivity of themagnetic sensor of FIG. 3A or 33, a magnetic member 20 such as ferriteis provided on the opposite side from the head H as shown to short onlythe magnetic paths of the respective elements to insulate them asexciting current paths between the elements, by which magnetic fluxentering from the head H of the main element 9 is caused to pass throughthe short-circuit path 20 and return to the head H through a pluralityof the auxiliary elements 10, 11 without leakage from the opposite endof the main element from the head, thereby to improve the directivitycharacteristic of the magnetic sensor.

FIGS. 5A to 5G illustrate another example, in which the magnetic sensorof three-dimensional construction in FIG. 4A is constructed in the formof a module. For example, as shown in FIG. 5A, elements 23 and 24 areattached on the upper side of a substrate 30 to copper foils 25 providedat the marginal portion of the substrate on the underside of which theelement 11 is similarly mounted.

While, as depicted in FIG. 5D, the elements 10 and 9 are attached tocopper foils 25 on both sides of a substrate 31 respectively. Then, thesubstrate are assembled together with spacers 26 therebetween into aunitary structure as shown in FIG. 5G. FIGS. SE, SE, and

FIGS. 5C, 5F (both shown in section) illustrate examples of the similarconstruction as FIGS. 5A, 5D, which is different in the arrangement oneach substrate from the above example but exactly identical therewith inthe final construction.

FIGS. 6A, 6B and 6C shows another example in which the magnetic sensorof FIG. 4A is constructed by using module substrate as in FIGS. 5A to5G. After the elements are attached to one side of each of the substrate30 and 31 such as depicted in FIG. 6A and 68 as described above inconnection with FIG. 5A to 5G, the both substrate are assembled togetherwith their cuts 28 engaged with each other as illustrated in FIG. 6C.

FIG. 7 illustrates another example in which a mag netic sensor similarto that of FIGS. 6A, 6B and 6C is constructed by using a hollow squaresubstrate 29 and in which the auxiliary inductance elements and the mainelement are held on the outside and inside of the substraterespectively.

With such a module construction, the magnetic sensor can also be readilyconstructed in a cubic form.

As has been described above, in the narrow beam type magnetic sensor ofthis invention, its magnetism detecting distribution curve can be madeextremely sharp to provide high resolution by appropriate selection ofthe distance D between the main element serving as a head for detectingmagnetic information and each of the auxiliary elements and the distanced between the winding end of the main element and those of the auxiliaryelements. Therefore, the magnetic sensor of this invention is capable ofdiscriminating magnetic signals of high density, small in size and highin reliability, and hence is extremely effective for inclustrialpurposes.

FIG. 8 is a graph showing the magnetism detecting distribution curve IIof the prior single type magnetic sensor depicted in FIG. 1 and that Iof the magnetic sensor of this invention in FIG. 3A or 3B which weremeasured in the case of D=l mm and d=l.5 mm, and it will be understoodfrom the graph that the narrow beam type construction is remarked byexcellent. With the narrow beam type construction shown in FIG. 3A or 3Bthe detecting resolution is high in the direction of the line Y-Ya butno so much high in the direction of the axis X-Xa (refer to FIGS. 4A, 4Band 4C) perpendicular to that Y-Ya. Then, the use of the constructionsuch as depicted in a construction shown in FIG. 4A makes the detectingdistribution curve in the direction of the axis X-Xa sharp and providesa magnetic sensor having a sharp detecting distribution curve in athree-dimensional manner.

The magnetic sensor of this invention serves as a highly excellentmagnetism detecting head of high resolution when employed forreading-out of magnetic records.

What we claim is:

l. A magnetic sensor using a parametrically excited second harmonicoscillator, in which at least one inductance element is formed with amagnetic wire member having a magnetic film deposited on a conductor anda winding wound thereon; in which a capacitor is connected in parallelwith the winding to constitute a resonance circuit; an AC excitingcurrent is applied to the magnetic wire member to produce a secondharmonic of the exciting current in the resonance circuit; whereby aminute magnetic field is detected by utilizing a change in the phase ofthe second harmonic in accordance with the direction of an externalmagnetic field; the improvement of the magnetic sensor, characterized inthat at least three inductance elements each formed with a magnetic wiremember and its winding are employed, one of them being a main elementand the others auxiliary elements; the auxiliary elements being disposedabout the main element; and the windings of the elements beinginterconnected in series in such a manner that when the same excitingvoltage is applied to the magnetic members a magnetic field establishedby a second harmonic current flowing in the winding of the main elementand a magnetic field by the second harmonic current flowing in thewinding of each auxiliary element may be opposite in direction to eachother whereby a sensitivity characteristic against an external magneticfield is made extremely sharp with respect to a head portion of one endof the main element.

2. A magnetic sensor according to claim 1, in which three inductanceelements are employed, the magnetic wire members of the three inductanceelements are arranged in parallel in equal spaces and connected inseries to one another so that a center one of the inductance elements isthe main element.

3. A magnetic sensor according to claim 1, in which three inductanceelements are employed, the magnetic wire members of three inductanceelements are arranged in parallel in equal spaces and connected inparallel to one another so that a center one of the inductance elementsis the main element.

4. A magnetic sensor according to claim 1, in which in that fiveinductance elements are employed, the magnetic wire members of four ofthe five inductance elements are arranged in parallel along edge linesof a regular rectangular solid while the magnetic wire member of one ofthe five inductance elements are arranged along the center axis of theregular rectangular solid.

5. A magnetic sensor according to claim 1, in which the magnetic wiremembers are disposed on at least one substrate of micromodule.

1. A magnetic sensor using a parametrically excited second harmonicoscillator, in which at least one inductance element is formed with amagnetic wire member having a magnetic film deposited on a conductor anda winding wound thereon; in which a capacitor is connected in parallelwith the winding to constitute a resonance circuit; an AC excitingcurrent is applied to the magnetic wire member to produce a secondharmonic of the exciting current in the resonance circuit; whereby aminute magnetic field is detected by utilizing a change in the phase ofthe second harmonic in accordance with the direction of an externalmagnetic field; the improvement of the magnetic sensor, characterized inthat at least three inductance elements each formed with a magnetic wiremember and its winding are employed, one of them being a main elementand the others auxiliary elements; the auxiliary elements being disposedabout the main element; and the windings of the elements beinginterconnected in series in such a manner that when the same excitingvoltage is applied to the magnetic members a magnetic field establishedby a second harmonic current flowing in the winding of the main elementand a magnetic field by the second harmonic current flowing in thewinding of each auxiliary element may be opposite in direction to eachother whereby a sensitivity characteristic against an external magneticfield is made exTremely sharp with respect to a head portion of one endof the main element.
 2. A magnetic sensor according to claim 1, in whichthree inductance elements are employed, the magnetic wire members of thethree inductance elements are arranged in parallel in equal spaces andconnected in series to one another so that a center one of theinductance elements is the main element.
 3. A magnetic sensor accordingto claim 1, in which three inductance elements are employed, themagnetic wire members of three inductance elements are arranged inparallel in equal spaces and connected in parallel to one another sothat a center one of the inductance elements is the main element.
 4. Amagnetic sensor according to claim 1, in which in that five inductanceelements are employed, the magnetic wire members of four of the fiveinductance elements are arranged in parallel along edge lines of aregular rectangular solid while the magnetic wire member of one of thefive inductance elements are arranged along the center axis of theregular rectangular solid.
 5. A magnetic sensor according to claim 1, inwhich the magnetic wire members are disposed on at least one substrateof micromodule.